It has heretofore been known that the isomerization of paraffins, such as n-hexane, to equilibrium mixtures of branched chain isomers, substantially increases the octane rating of the paraffin hydrocarbons. Prior art processes dealing with paraffin isomerization include a liquid-phase process utilizing a catalyst containing an aluminum chloride dissolved in antimony trichloride, which, together with HCl formed during the reaction, are corrosive. Another process, referred to as the Penex process, which has been used for isomerizing pentane and hexane fractions from refinery naphthas and natural gasolines in the presence of hydrogen and a platinum containing catalyst requires the continuous addition to the feed of an organic chloride which also produces HCl. Another process involves reaction of a pentane/hexane feed in the presence of hydrogen and a catalyst containing platinum highly dispersed on hydrogen mordenite at a pressure of 150-350 psi and a temperature of 400 to 550° F., with a maximum water level in the feed of 50 ppm. The above processes have been costly to operate because of extensive corrosive effects attributable to the use of highly acidic catalysts or by-products arising from use of such catalyst, thereby requiring expensive alloy equipment. Moreover, moisture and high molecular weight hydrocarbons usually present as contaminants in the charge stock cause deterioration of the catalyst and necessitate frequent replacement thereof. Another process which has been carried out at a higher temperature of 700 to 800° F. utilizes a catalyst such as platinum on a silica-alumina base in the presence of hydrogen. At the high temperatures required, the equilibrium mixture of isomers is such that substantial recycling of a portion of the paraffin feed is necessary to obtain the desired improvement in octane rating.
U.S. Pat. No. 4,374,296 discloses a process for upgrading normal paraffinic hydrocarbons or cycloparaffins by hydroisomerization in the presence of a specified highly siliceous porous zeolite crystalline material of enhanced acid activity having a minor proportion of a Group VIII metal combined therewith. In addition, the invention described therein involves continuous hydroisomerization of normal paraffins or cycloparaffins for extended periods of time in the presence of hydrogen and the above indicated catalyst so as to produce a mixture of branched chain isomers having a high octane rating without the use of corrosion resistant alloy equipment or frequent replacement of catalyst material. In addition, the invention is directed to the hydroisomerization of light paraffinic hydrocarbons such as n-pentane, n-hexane or mixtures thereof in the presence of hydrogen and a specified catalyst comprising a porous crystalline zeolite of enhanced acid activity and defined silica/alumina mole ratio and constraint index and having a minor proportion of platinum, supported on an alumina carrier under specified reaction conditions.
As the demand for diesel fuel increases worldwide there is increasing interest in sources other than petroleum crude oil for producing diesel fuel. One such non-petroleum source is what has been termed renewable sources. These renewable sources include, but are not limited to, plant oils such as corn, palm oil, rapeseed, canola, soybean and algal oils, animal fats such as inedible tallow, fish oils and various waste streams such as yellow and brown greases and sewage sludge. The common feature of these sources is that they are composed of triglycerides and Free Fatty Acids (FFA). Both of these compounds contain n-paraffin chains having from about 8 to about 24 carbon atoms. The n-paraffin chains in the tri-glycerides or FFAs can also be mono-, di- or poly-unsaturated. Some of the glycerides from the renewable sources may be monoglycerides or diglycerides instead of or in addition to the trigylcerides.
There are reports in the art disclosing the production of hydrocarbons from oils. For example, U.S. Pat. No. 4,300,009 discloses the use of crystalline aluminosilicate zeolites to convert plant oils such as corn oil to hydrocarbons such as gasoline and chemicals such as para-xylene. U.S. Pat. No. 4,992,605 discloses the production of hydrocarbon products in the diesel boiling range by hydroprocessing vegetable oils such as canola or sunflower oil. Finally, U.S. 2004/0230085 A1 discloses a process for treating a hydrocarbon component of biological origin by hydrodeoxygenation followed by isomerization. Undesired oxygen is typically removed from fatty acids or their esters by deoxygenation reactions. The deoxygenation of bio oils and fats, which are oils and fats based on biological material, to produce hydrocarbons suitable as diesel fuel products, may be carried out by catalytic hydroprocessing, such as hydrocracking, but also more controlled hydrotreating conditions may be utilized.
Presently, hydroisomerization catalysis typically involves a bi-functional catalyst with an acid function, and a precious metal (PM) function. Acidity is usually provided by a molecular sieve component (zeolite, silico-alumino-phosphates, etc.), and the PM function is very often provided by platinum deposited on the catalyst. Molecular sieves used in currently available catalysts are provided with specific content of aluminum or silica to control the acidity. These catalysts show very good activity, but also suffer from relatively high cracking, such that a catalyst passivation step using molecules such as tert-butyl amine (TBA) is used to control the acidity and thus improve the process yield.